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diff --git a/src/dctv/mmap.h b/src/dctv/mmap.h
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+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#pragma once
+#include "dctv.h"
+
+#include <utility>
+#include <sys/mman.h>
+
+#include "bitbash.h"
+
+namespace dctv {
+
+// Basic handle to a region of address space managed with mmap or
+// something like mmap.  The mapping's size is rounded up to whatever
+// the current system's allocation granularity is, and the size
+// reported by the mapping is this expanded size.
+struct Mmap : NoCopy {
+  inline constexpr Mmap(Mmap&& other) noexcept;
+  inline constexpr Mmap& operator=(Mmap&& other) noexcept;
+  inline ~Mmap() noexcept;
+
+  static Mmap map(
+      void* addr,
+      size_t nbytes,
+      int prot,
+      int flags,
+      int fd,
+      off_t offset);
+
+  static Mmap anonymous(size_t nbytes);
+
+  inline void* addr() const noexcept;
+  inline size_t nbytes() const noexcept;
+
+  inline void release() noexcept;  // Stop managing the memory region
+
+ protected:
+  inline Mmap(void* addr, size_t nbytes) noexcept;
+  void do_unmap() noexcept;
+  void* addr_;
+  size_t nbytes_;
+};
+
+// A memory mapping that can be mapped into several places in virtual
+// memory at once without copying the underlying bytes.
+struct MmapShared : Mmap {
+  // Make a new mapping of the given size somewhere.  If NEW_ADDR is
+  // non-nullptr, place the mapping at NEW_ADDR.
+  static MmapShared make(size_t nbytes, void* new_addr = nullptr);
+
+  // Make a new mapping backed by a file.
+  static MmapShared of_file(int fd, size_t nbytes, int prot);
+
+  // Create another mapping of this memory at a specific location.
+  // If NEW_ADDR is nullptr, the OS picks the new location.
+  // If NEW_NBYTES is zero, it defaults to the size of this mapping.
+  // NEW_NBYTES is the size of the new mapping, which can be smaller
+  // than the source.
+  MmapShared dup(void* new_addr = nullptr,
+                 size_t new_nbytes = 0);
+
+  // Resize this mapping while preserving contents.  May change the
+  // base address of the mapping!
+  void resize(size_t new_nbytes);
+
+ private:
+  explicit inline MmapShared(Mmap&& mmap) noexcept;
+  inline MmapShared(void* addr, size_t nbytes) noexcept;
+};
+
+// The const attribute here helps the compiler prevent re-reads of
+// cached_page_size.
+extern const size_t cached_page_size;
+__attribute__((const)) inline size_t page_size() noexcept;
+
+inline size_t mmap_round_size_up(size_t nbytes) noexcept;
+inline size_t mmap_round_size_down(size_t nbytes) noexcept;
+inline bool mmap_aligned_p(size_t bytes) noexcept;
+
+}  // namespace dctv
+
+#include "mmap-inl.h"